Radiation therapy involves the transmission of radiation energy to a tumor site (or volume-of-interest) within the patient to control cell growth. Radiation therapy may be curative in a number of types of cancer if they are localized to one area of the body.
Radiation therapy treatment planning may be carried out according to a forward planning technique or an inverse planning technique. Forward planning involves delivering an initial planned radiation dose and then delivering subsequent doses by observation or inference of the efficacy of the preceding dose in a trial-and-error manner. The determination of dose delivery by forward planning is therefore performed according to human observation and experience. Inverse planning instead seeks to calculate an optimized dose delivery and then work backwards to determine the appropriate radiation beam characteristics to deliver that optimized dose. Inverse planning of radiation therapy for tumors may be performed for Tomotherapy, or other Intensity Modulated Radiation Therapy (IMRT) radiation delivery techniques employing ionizing photon radiation or any other ionizing radiation like e.g. protons, heavy ions, or electrons. These techniques involve transmission of radiation beams, usually collimated by an appropriate collimation device like a multi-leaf collimator (MLC), toward the volume-of-interest (VOI) from various angular orientations.
Radiation dose can damage or kill both cancerous and healthy tissue cells. A radiation beam originating from a radiation source and projection through a subject will deposit radiation dose along its path. It is typical that some healthy tissue will receive radiation dose during a radiation treatment. In order to ensure that the patient is optimally treated, it is necessary to predict and shape a dose distribution in treatment planning of radiation therapy. Dose is deposited energy by some treatment devices applying ionizing radiation to a patient or measurement device (or in other words, VOI), and being computed in a point or a number of points. The dose at any given position inside a VOI is composed of a weighted superposition of elementary doses. Elementary dose is dose deposited during a certain time interval and/or a certain configuration of the treatment device.
Two quantities are of interest in treatment planning and form the basis of all planning algorithms:
1. The dose to any point in a VOI;
2. The derivative of a cost function of dose at any point with respect to its elementary constituents.
Current techniques for evaluating these two quantities are cumbersome and time-consuming. There is a desire for improvement of systems and methods for determining the above two quantities quickly and accurately, which is important not only for designing good radiation treatment plans, but also for the successful implementation of further interactive adaptive treatment techniques.